Viruses are the intracellular parasites that depend on synthetic processes of host cells. They cannot be grown on ordinary medium. Special microscopes are needed to visualize their structure, which consists of three main components:
1. Genome –genetic material consisting of DNA or RNA component but never both.
Most common are single stranded RNA and double stranded DNA viruses.
2. Surrounding capsid –proteinaceous in structure
3. Envelope –protein bilayer, not present in all viruses, those devoid are known as naked.
Additional to structural components, host cell surface receptors are present.
Glycoproteins are present for attachment to host.
Virus consisting of these main components is known as virion.
Virus Life Cycle
Series of processes facilitate entry of virus, which incorporates into nucleic acids, resulting in rapid replication. It damages human nucleic acid, producing toxic effects.
Antivirals are exclusively directed against viral nucleic acids and not humans, due to which chemoprophylaxis becomes difficult.
- Attachment to cell surface. Virus gets attached to host cell receptors.
- Once attached, structural proteins recognize.
- Binding of these two components lead to conformational changes.
- Lysoproteins are also recognized, fusion occurs.
- Penetration inside host cells takes place.
- Uncoating of virus occurs
- Once uncoating has occurred, genetic material is transcribed and translated within host nucleus
- Proteins are formed and budding of virus occurs.
Different antivirals target different steps of this life cycle.
Main difference between DNA and RNA viruses is of site. RNA viruses utilize own mRNA and not of host. Their own polymerases synthesize essential mRNA.
- Pox virus
- Herpes virus
- Adeno virus
- Papilloma virus
- Rubella virus
- Rhabdo virus
- Picorna virus
- Retro virus
Antiviral Drugs Classification
1. Drugs that inhibit uncoating of viral RNA
- Gamma globulins
- Nucleoside reverse transcriptase inhibitors (NRTIs)
- Non Nucleoside reverse transcriptase inhibitors (NNRTIs)
3. Drugs that inhibit late protein synthesis and processing
- Protease inhibitors
3. Agents to treat Hemorrhagic fevers (Dengue, Crimean congo,)
- Ribavirin (with anti-hepatitis agents, INF, also effective in influenza)
5. Agents to treat human papilloma virus infections (genital warts)
- Imiquiumod (topical )
6. Agents to treat Bird Flue
- Interferon alfa 2a
- Interferon alfa 2b
- Interferon alfa 2c
- Interferon Alfacon 1
- Peg Interferon alfa2a
- Peg interferon alfa2b
- Ribavirin ( oral )